1. Field of the Invention
The present invention relates to an antenna apparatus. More particularly, the present invention relates to an antenna apparatus capable of improving electromagnetic wave reception efficiency.
2. Description of the Related Art
In general, an antenna is an apparatus for converting an electric signal into electromagnetic wave energy to spatially radiate out or for receiving and converting electromagnetic wave energy into an electrical signal. Antennas may be classified into two types. A first type is a contact type antenna, which detects electromagnetic radiation in contact with a target object. A second type is a non-contact type antenna, which detects electromagnetic radiation separated from a target object.
Examples of use of a contact type antenna include a radiometer, a dielectric load detector for geological survey, a hyperthermia apparatus, a non-invasive detector, or a terminal probe for medical equipment.
A radiometer is a device for measuring the characteristics of an arbitrary electromagnetic medium and changes therein by receiving electromagnetic radiation from the electromagnetic medium at a frequency of about 1 GHz to 100 GHz. For example, a radiometer for a body is a device that passively receives and analyzes a radio frequency (RF) signal radiated from every electromagnetic medium having a temperature greater than absolute zero of the Kelvin scale by using a contact type antenna. A hyperthermia apparatus is a non-invasive treatment apparatus for radiating electromagnetic waves into the human body through a contact type antenna for therapeutic purposes. A geological survey apparatus or a non-invasive detection apparatus radiates signals into or receives signals from an object by contacting an antenna to the object to analyze the inside of the object.
Since the contact type antenna receives electromagnetic radiation while in contact with a target object to be measured, the initial position and angle of the antenna may be changed while it is in contact with the object. In a measuring apparatus using a conventional contact type antenna, a necessary signal (i.e., the signal intended to be received) is greatly affected by minor lobes due to unwanted noise in the boundary between free space and the object. In particular, in a radiometer for processing a weak RF signal, electromagnetic noise due to such minor lobes seriously affects the entire system, even if the noise level may be very low.
Many attempts have been made to improve the directional gain in a conventional contact type antenna. The type of antenna, however, limits gain improvement. Dynamics of a radiation pattern from an arbitrary medium in contact with the antenna is another consideration.
In the context of the present invention, the term xe2x80x9cgainxe2x80x9d indicates the extent to which radio waves radiate in a particular desired direction. A xe2x80x9cmain lobexe2x80x9d indicates most of the electromagnetic field transmitted or received via an antenna, which radiates in a particular direction. A xe2x80x9cminor lobexe2x80x9d indicates a weak electromagnetic field pattern radiated or received via an antenna, which radiates in another direction.
Rapid advances in the electronics industry have seriously increased noise in almost all frequency bands. For this reason, some radiometer designers are searching for frequency bands that are less affected by noise for use in new systems. A particular frequency band, however, is required for a particular function of equipment using an antenna, such as a radiometer. Therefore, there is a need to develop a high-gain antenna apparatus that is less affected by external noise and has improved accuracy and reliability. To improve the gain and electromagnetic reception efficiency of the antenna, an antenna apparatus capable of suppressing signal loss via the antenna and capable of blocking noise is needed.
In an effort to solve the above problems, it is a feature of an embodiment of the present invention to provide an antenna apparatus with improved reception efficiency, capable of blocking noise from entering via an antenna thereof.
To provide this feature of an embodiment of the present invention, there is provided an antenna apparatus including: an antenna for receiving electromagnetic radiation from an object to be measured; and a condensing element, which is constructed to surround the antenna, which is located at a center of the condensing element, wherein the condensing element reflects and condenses the electromagnetic radiation toward the antenna.
Preferably, the antenna is a contact type antenna that directly contacts the object to be measured. The condensing element is preferably formed of a conductive metal.
Preferably, the condensing element includes: an interior wall including an electromagnetic reflecting material to reflect and converge the electromagnetic radiation toward the antenna; an exterior wall including an electromagnetic reflecting material to shield external electromagnetic radiation not originating from the object to be measured; and an intermediate wall between the interior wall and the exterior wall, which includes at least one groove formed to a predetermined depth in a direction of wave propagation. In the antenna apparatus, the interior wall may be semi-spherical, spherical, or cylindrical.
Preferably, the interior wall and the exterior wall have different heights. Alternatively, the interior wall and the exterior wall may have an equal height.
Also preferably, the at least one groove contains an electromagnetic reflecting material or an electromagnetic absorbing material on an inner surface thereof.
Preferably, a top surface of the intermediate wall is inclined toward the antenna.